Journal of Magnetism and Magnetic Materials 93 (1991) 95-100 95 North-Holland Magnetoresistance of Fe/Cr superlattices F. Petroff, A. Barth616my, A. Hamzi6, A. Fert Laboratoire de Physique des Solides, Unicersit~ Paris-Sud, 91405 Orsay, France P. Etienne, S. Lequien and G. Creuzet L.C.R. Thomson CSF, 91404 Orsay, France In light of new experimental data on Fe(001)/Cr(001) superlattices, we discuss the role of the main parameters involved in the giant magnetoresistance: thicknesses, interface roughness and temperature. 1. Introduction The giant magnetoresistance (GMR) of the magnetic superlattices-due to a spin t,alL,e effect-has been discovered two years ago in Fe(001)/Cr(001) superlattices [1, 2] and has been recently investigated in several systems: not only Fe/Cr [1-6], but also Co/Ru [4], Au/Co [3, 7, 8] and several other microstructures composed of layers of Co, Fe or Ni-based alloys separated by noble metals [9, 10]. In all these systems there is a large magnetoresistance because the resistivity is higher when the magnetization of neighbor layers are antiparallel. In superlattices such as Fe/Cr the antiparallel orientations are due to antiferro- magnetic interlayer couplings. Two theoretical models have been worked out [11, 12]. In this paper we present new experiments results on Fe(001)/Cr(001) superlattices bringing the im- portant parameters of the GMR into light. We will first discuss the thickness dependence of the GMR and then the role of the interface mi- crostructure (we present data on the reduction of the GMR by interface sharpening and its en- hancement by thermal annealing or interfacial mixing). Finally we present data showing that the existence of a large magnetoresistance is gener- ally correlated with an enhancement of the tem- perature dependence of the resistivity. We describe a simple model based on electron scat- tering by spin waves that explains this correlation and also accounts for the temperature dependence of the GMR. 2. Thickness dependence of the magnetoresistance The first important parameter that determines the magnitude of the GMR is the thickness of the layers. The GMR decreases very rapidly as the chromium thickness increases (see fig. la) and varies more softly with the thickness of iron [1, 3]. It appears from physical arguments [2] and theo- retical analyses [11, 12] that the major parameter is the ratio of the chromium thickness to the electron mean free path: too thick a chromium layer suppresses the interplay between scattering processes at its two interfaces (the two interfaces act in two independent current channels). Fig. lb shows that theory predicts the right thickness dependence. 113114-8853/91/$03.50 © 1991 -Elsevier Science Publishers B.V. (North-Holland)